1. Field of the Invention
The present invention is directed to a process for the production of polyisocyanates by the phosgenation of polyamines using a special mixer.
2. Description of the Prior Art
In chemical technology, polyisocyanates are primarily produced by the conversion of primary amines with phosgene, wherein both reaction components are customarily dissolved or suspended in a suitable solvent.
The efficiency of mixing these reaction components considerably influences the degree of purity of the product. The purity also depends on the kind of mixer and whether the product is formed without clumps or caking.
Special nozzle arrangements have been used for this purpose (DE-PS No. 1,792,660 corresponding to GB-PS No. 1,238,669; DE-OS No. 2,950,216 corresponding to U.S. Pat. No. 4,289,732: EP-OS No. 65,727 corresponding to U.S. Pat. No. 4,419,295) as well as pumps such as centrifugal pumps (DE-PS No. 2,153,268 corresponding to U.S. Pat. No. 3,947,484). In spite of all efforts, the formation of clumps and blockages cannot be avoided during mixing of the two components.
Accordingly, it is an object of the present invention to be able to prepare polyisocyanates by the phosgenation of polyamines without the formation of clumps or cakes. This object may be achieved in accordance with the process of the present invention as set forth hereinafter.